Heretofore there have been very few particular type dental service equipment that can practically be used for the purpose of dental group examination, for instance in schools and offices. Thus the realities are that dentists with a reflex mirror on their forehead have to sit their patient on a conventional type dental chair and look from one side into the cavity of his mouth under the insufficiently reflected light of the mirror at their slightly slouched posture. This has the results in dentists not being able to always find out the affected parts of a patient's teeth and/or teethbridge nor check any delicately affected parts to the fullest extent. Besides, they get easily fatigued due to their slouched posture that must be kept for a long length of time running so that as they examine the mouth cavity of a patient after another, who are waiting at the tail of a queue, they are increasigly liable to overlook the patients' affected parts or provide an erroneous diagnosis.